KR101465300B1 - Poly amic acid composition comprising graphane oxide and preparation method thereof - Google Patents

Abstract

The present invention relates to a polyamic acid composition comprising graphene oxide in which some of the oxide groups are reduced and a method for producing the same. More specifically, the present invention provides a polyimide film comprising a polyamic acid composition comprising graphene oxide wherein a part of the oxide groups are reduced according to the present invention, and when the polyimide film is produced, the polyimide film is improved not only in mechanical strength but also in electric conductivity This is possible. In the reduction, the reducing agent is reduced by at least one reducing agent selected from the group consisting of N, N-dimethylformamide (DMF), hydrazine and L-ascorbic acid. Thus, when the polyimide film including the polyamic acid composition is prepared and applied to the IT, electronic, and aerospace industries, the related industry is dramatically developed.

Description

The present invention relates to a polyamic acid composition containing graphene oxide and a preparation method thereof,

TECHNICAL FIELD The present invention relates to a polyamic acid composition containing graphene oxide and a method for producing the same, and more particularly, to a polyamic acid composition and a polyimide film produced by the method, which can improve electrical conductivity and mechanical strength.

Polyimide is a key core material in the IT and aerospace sectors due to its high thermal stability and effective mechanical properties. The polyimide film is used as an advanced high-functional industrial material which can withstand a high temperature of 400 ° C or higher and a low temperature of minus 269 ° C, and is thin and flexible. It is also widely used in fields requiring stable performance in a harsh environment due to its strong chemical resistance and abrasion resistance. Initially, it was developed and used as a material for the aerospace sector, and gradually expanded its use to industrial equipment and the electronics industry. Therefore, it is currently used in a disk of flexible printed circuit board (FPCB) in LCD, PDP TV, cellular phone, and digital camera.

However, such a polyimide film has a problem that excellent electrical conductivity and mechanical strength are required. Thus, research on the improvement of the electrical conductivity and the mechanical strength is active, but there is still a problem in improving the electrical conductivity and the mechanical strength by a more innovative method.

It is an object of the present invention to provide a polyamic acid composition capable of dramatically improving electrical conductivity and mechanical strength and a polyimide film produced thereby.

According to an aspect of the present invention, there is provided a polyamic acid composition comprising graphene oxide having a reduced amount of oxide groups. In addition, the graphene oxide in which a part of the above-mentioned oxides are reduced is a peak having a peak height of not more than 70% formed at 550 to 580 eV when measuring X-ray photoelectron spectroscopy (XPS) binding energy to non- And has a height. Further, the reduction is characterized in that it is reduced through any one or more reducing agents selected from the group consisting of N, N-dimethylformamide (DMF), hydrazine and L-ascorbic acid . Wherein the partially reduced graphene oxide is 3 parts by weight to 7 parts by weight based on 100 parts by weight of the polyamic acid.

A polyimide film according to another aspect of the present invention is prepared by including the polyamic acid composition.

A method for producing a polyamic acid composition according to another aspect of the present invention includes the steps of (1) oxidizing graphite to produce graphene oxide, (2) reducing a portion of the graphene oxide, and (3) And adding the reduced graphene oxide to the polyamic acid. Further, the method may further include ultrasonic treatment to reduce the graphene oxide evenly between the step (1) and the step (2). And further comprising a heat treatment step at 50 to 250 DEG C after the step (3). The reduction is characterized by reducing 30% to 80% of the oxide groups. Further, the reduction is characterized in that it is reduced through any one or more reducing agents selected from the group consisting of N, N-dimethylformamide (DMF), hydrazine and L-ascorbic acid . And the partially reduced graphene oxide is 3 to 7 parts by weight based on 100 parts by weight of the polyamic acid.

When a polyimide film is prepared by using the polyamic acid composition according to the present invention, a polyimide film having remarkably improved electrical conductivity and mechanical strength can be provided. Providing such a polyimide film to various industrial fields such as aerospace and electronic industry will lead to the overall development of related industries.

FIG. 1 is a photograph of a section of a polyimide film according to Example 1, Example 5, Example 6, Comparative Example 1 and Comparative Example 2 observed with an FE-SEM (Hitachi S-4800).
2 is a photograph of the surface of a polyimide film according to Examples 1, 5, 6, and Comparative Example 2, observed with TEM.
3 is a graph showing the results of measuring the mechanical strengths of the respective polyimide films according to Examples 1, 5 and 6 and Comparative Examples 1 and 2 according to the present invention.
4 is a graph showing the results of measuring the electrical conductivities of Examples 1, 5, and 6 and Comparative Example 2 according to the present invention.
5 is a graph showing changes in mechanical strength with changes in the content of graphene oxide in Examples 1, 2, 3, and 4 according to the present invention.
6 is a photograph showing SEM images of polyimide cross-sections according to changes in the content of graphene oxide in Examples 1, 2, 3, and 4 according to the present invention.
FIG. 7 is a graph showing the results of X-ray photoelectron spectroscopy (XPS) analysis for Examples 1, 5, and 6 and Comparative Example 2 according to the present invention.

Accordingly, the present inventors have made intensive studies to overcome the problems of the prior art. As a result, the present inventors have found that a polyamic acid composition comprising graphene oxide in which some of the oxide groups according to the present invention are reduced and a polyimide film It is possible to improve the electrical conductivity and the mechanical strength of the polyimide film, and the present invention has been completed.

In general, polyimide films are widely used in the aerospace field and the electronic field. Polyimide films widely used in this manner are more excellent polyimide films as electrical conductivity and mechanical strength are improved. Also, poly amic acid (PAA) corresponds to a precursor of the polyimide.

The polyamic acid composition according to the present invention may contain graphene oxide in which some of the oxide groups are reduced. It is preferable to oxidize the graphite because it is not well dispersed even when mixed with the polymer due to van der Waals bonding between the wide surface and the surface. Through such oxidation, graphene oxide containing oxide groups is formed. These oxide groups allow dispersion to be achieved when the graphene oxide is mixed with the polymer. Particularly, when it is mixed with the polyamic acid which is a precursor of polyimide, it is dispersed well and serves to improve the mechanical strength of the finally obtained polyimide. However, when the polyimide film is produced using the polyamic acid composition in which the graphen oxide is mixed, the electrical conductivity can not be improved even if the mechanical strength is improved. Thus, when a polyamic acid composition containing only graphene oxide is produced, a polyimide film that does not have improved electrical conductivity is provided in a polyimide film that simultaneously requires excellent mechanical strength and excellent electrical conductivity.

However, when a polyimide film is produced using a polyamic acid composition containing graphene oxide in which some of the oxide groups are reduced as in the present invention, it is possible to produce a polyimide film having improved mechanical strength and electrical conductivity at the same time.

The peak height formed at 550 to 580 eV when X-ray photoelectron spectroscopy (XPS) binding energy is measured with respect to non-reduced graphene oxide is preferably 70% or less Lt; / RTI > peak height. The ability to have a peak height of less than 70% means that at least 30% of the oxide groups are reduced. If the polyimide film is produced with graphene oxide in which the peak height of the partially reduced graphene oxide exceeds 70%, the electric conductivity is hardly significantly improved.

The reduction may be preferably carried out through any one or more reducing agents selected from the group consisting of N, N-dimethylformamide (DMF), hydrazine and L-acroic acid have.

In the case of reduction with N, N-dimethylformamide (DMF), when the content of the reduced graphene oxide, which is one of the preferred embodiments of the present invention, is 5 parts by weight , A tensile modulus of 25 GPa or more, a tensile strength of 1100 Mpa or more, an elongation of 7.5% or more, and an electrical conductivity of 10 ^-5 Scm ^-1 or more. When the content of graphene oxide is reduced to 5 parts by weight, the tensile elastic modulus is at least 15 GPa, the tensile strength is at least 750 MPa, An elongation of 10% or more, and an electrical conductivity of 10 ^-2.5 Scm ^-1 or more. When L-acroic acid is used as the reducing agent, the content of graphene oxide in which a part of the oxide groups, which is one of the preferred embodiments of the present invention, is reduced to 5 parts by weight, A tensile strength of 400 Mpa or more, an elongation of 5% or more, and an electrical conductivity of 10 ^-1 Scm ^-1 or more.

The partially reduced graphene oxide is preferably mixed with 3 parts by weight to 7 parts by weight with respect to 100 parts by weight of the polyamic acid. When the partially reduced graphene oxide is added in an amount of less than 3 parts by weight, the mechanical strength is excellent, but sufficient electrical conductivity is not imparted to the polyimide film. Further, when the above-mentioned partially reduced graphene oxide is added in an amount exceeding 7 parts by weight, the mechanical strength is lowered, which is undesirable.

As another feature of the present invention, the polyimide film may be one comprising the polyamic acid composition.

According to another aspect of the present invention, there is provided a method for producing a polyamic acid composition, comprising the steps of: (1) oxidizing graphite to prepare graphene oxide; The graphite can be preferably obtained by a mechanical or chemical method, more preferably by a chemical method. When the graphite is obtained by the chemical method, the cost is low, the yield is high, and mass production is possible. The graphite has van der Waals bond between a wide surface and a surface and is not well dispersed even when mixed with a polymer. Thus, it is preferable to oxidize the graphite to prepare an oxide group-containing graphene oxide and to mix it with the polymer. The oxidation may preferably be oxidized using potassium permanganate (kMnO 4) or sodium nitrate (NaNO 3) as an oxidizing agent. The oxidizing method using the oxidizing agent may include all the usual oxidizing methods, but may be carried out by using at least one solvent selected from the group consisting of sulfuric acid, hydrochloric acid, water, and hydrogen peroxide as the solvent. Further, the mixing of the oxidizing agent and the solvent may be performed by mixing the oxidizing agent in an amount of preferably 35 to 70 parts by weight based on 100 parts by weight of the solvent. If the amount of the oxidizing agent is less than 35 parts by weight, it is difficult to achieve a sufficient oxidizing effect. If the amount of the oxidizing agent is more than 70 parts by weight, the amount of the oxidizing agent remaining unoxidized is decreased. The treatment time of the oxidation is preferably 60 to 180 minutes. When the oxidation treatment time is less than 60 minutes, a sufficient time for oxidation is not guaranteed, which is undesirable. If the oxidation treatment time exceeds 180 minutes, it takes a long time, which is not preferable. By this oxidation, the graphite becomes a graphen oxide. The oxidized graphene oxide has an oxygen functional group such as OH or COOH introduced therein, and has a property of being well dispersed in an organic solvent by the oxygen functional group. As a result, even when mixed with a polymer, the dispersion easily occurs. When the polyimide film is produced with the oxidized graphene oxide, the mechanical strength of the final polyimide film is improved. However, there is a disadvantage that the polyimide film finally produced is not sufficiently imparted with electrical conductivity by the oxidation alone.

And (2) a step of reducing a portion of the graphene oxide to thereby impart electrical conductivity. When the polyimide film is produced by adding the partially reduced graphene oxide to the polyamic acid, which is a precursor of the polyimide, the resulting polyimide film has excellent electrical conductivity . Also, the reduction of the above part means that some oxygen functional groups present in the graphene oxide are removed. The functional groups not removed in addition to the removed oxygen functional groups facilitate the dispersion of the graphene oxide in the polyamic acid which is a precursor of the polyimide and function to simultaneously improve the electrical conductivity and the mechanical strength of the finally produced polyimide film. The reduction can be preferably reduced through any one or more reducing agents selected from the group consisting of N, N-dimethylformamide (DMF), hydrazine, and L-acroic acid . In the case of reduction with N, N-dimethylformamide (DMF), when the content of the reduced graphene oxide, which is one of the preferred embodiments of the present invention, is 5 parts by weight , A tensile modulus of 25 GPa or more, a tensile strength of 1100 Mpa or more, an elongation of 7.5% or more, and an electrical conductivity of 10 ^-5 Scm ^-1 or more. When the content of graphene oxide is reduced to 5 parts by weight, the tensile elastic modulus is at least 15 GPa, the tensile strength is at least 750 MPa, An elongation of 10% or more, and an electrical conductivity of 10 ^-2.5 Scm ^-1 or more. When L-acroic acid is used as the reducing agent, the content of graphene oxide in which a part of the oxide groups, which is one of the preferred embodiments of the present invention, is reduced to 5 parts by weight, A tensile strength of 400 Mpa or more, an elongation of 5% or more, and an electrical conductivity of 10 ^-1 Scm ^-1 or more.

The reducing method with the reducing agent may include all the general reduction methods, but water or distilled water may be preferably used as the solvent. The reducing agent and the solvent may be mixed with each other in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the solvent. If the amount of the reducing agent is less than 0.1 parts by weight, it is difficult to achieve a sufficient reduction effect. If the reducing agent is added in an amount of more than 50 parts by weight, the amount of the reducing agent remaining increases. The treatment time for the reduction is preferably from 1 hour to 30 hours. If the reduction treatment time is less than 1 hour, a sufficient reduction time can not be guaranteed, which is not preferable. If the reduction treatment time exceeds 30 hours, it takes too much time.

The partially reduced graphene oxide is preferably mixed with 3 parts by weight to 7 parts by weight with respect to 100 parts by weight of the polyamic acid. When the partially reduced graphene oxide is added in an amount of less than 3 parts by weight, the mechanical strength is excellent, but sufficient electrical conductivity is not imparted to the polyimide film. Further, when the above-mentioned partially reduced graphene oxide is added in an amount exceeding 7 parts by weight, the mechanical strength is lowered, which is undesirable.

In addition, the reduction preferably reduces 30% to 80% of the oxide groups, and when the reduction is less than 30%, it is difficult to impart sufficient electrical conductivity, and when the reduction is more than 80% It becomes difficult to achieve the mechanical strength.

Preferably, the method further comprises ultrasonic-treating the graphene oxide between steps (1) and (2). When the ultrasonic wave treatment step is further included, there is an effect that the gap between the plate and the plate of the graphene oxide is further enlarged and uniformly reduced on the plate.

(2) after the step of reducing the part of the graphene oxide or, preferably, further performing the ultrasonic treatment step in the step (1) and the step (2), (3) the step of reducing the partially reduced graphene oxide to the polyamic acid To the substrate.

Further, it is preferable that the step (3) further includes a heat treatment step. When the heat treatment step is further included, the electrical conductivity and the mechanical strength of the polyimide film are improved more effectively. Also, the heat treatment step is preferably performed at 50 to 250 ° C. Since the bubbling may occur in the film when the heat is suddenly raised in the heat treatment step, it is preferable to gradually raise the temperature from 50 ° C to 250 ° C.

When a polyamic acid composition is prepared by the method for producing a polyamic acid composition according to the present invention and a polyimide film is prepared using such a composition, it is possible to provide an excellent polyimide film having improved mechanical strength and electrical conductivity at the same time.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example

Example  One

Pyromellitic dianhydride (PMDA), obtained from Sigma Aldrich, was dried under vacuum at 120 < 0 > C. Also, 4,4-oxydianiline (ODA) and dimethylacetamide (DMAc) were supplied by Sigma Aldridge. Also, the graphite having a particle size of 20 to 25 μm and a purity of 99.5% was supplied from Samjung C & C Inc., Korea. H 2 SO 4, HCl, H 2 O 2, KMnO 4 and NaNO 3 were purchased from Sigma Aldrich. Also, hydrazine, L-ascorbic acid and N, N-dimethylformamide (DMF) were obtained from Junsei Chemical Co., Japan.

Graphene oxide was synthesized by oxidation of graphite using the Hummers method. Specifically, 4 g of graphite, 2 g of sodium nitrate and 12 g of potassium permanganate were added to a 500 ml round bottom flask containing 100 ml of sulfuric acid. The mixture was stirred for one hour and then immersed in an ice bath for the first time. It was then slowly heated to 35 [deg.] C for 3 hours. Then 200 ml of deionized (DI) water was added. After 30 minutes, 30% hydrogen peroxide was added to reduce unreacted potassium permanganate. The mixture was filtered through a membrane filter having a pore size of 0.2 mu m. It was washed with diluted hydrochloric acid and deionized water. The thus prepared graphene oxide was dried at 40 DEG C for 48 hours.

After that, 50 mg of the graphene oxide was sonicated for 30 minutes (Sonic Vibracell, VCX-750, 60 Hz) using N, N-dimethylformamide (DMF) as a reducing agent. ) Was dispersed in 100 ml of N, N-dimethylformamide (DMF). The mixture was then heated in an oil bath at 153 DEG C for 1 hour. After stopping, it was filtered with a membrane filter, and then washed repeatedly with demineralized water to remove excess N, N-dimethylformamide (DMF). Finally, the graphene oxide, in which some of the oxide groups were reduced by N, N-dimethylformamide (DMF), was dried under vacuum.

For the synthesis of polyamic acid, 2 g of ODA was first dissolved in 40 ml of DMAc using a stirrer. 2.16 g of PMDA was added to the ODA solution. And the mixture was stirred at room temperature in an N2-purged glove box for 24 hours. Through this process, a sticky pure polyamic acid solution was obtained. This pure polyamic acid was mixed with a suspension of DMAc and graphene / DMAc (1 mg ml-1). At this time, the polyamic acid composition including the graphene oxide in which some of the oxide groups were reduced was mixed with 5 parts by weight of the polyamic acid based on 100 parts by weight of the polyamic acid. The polyamic acid composition was cast on a glass plate and DMAc was removed by slowly heating to complete the polyimide film.

Example  2

In the preparation of the polyamic acid composition, 1 part by weight of reduced graphene oxide was added to a pure polyamic acid solution mixed with a suspension of graphene / DMAc (1 mg ml-1) The polyimide film was completed in the same manner as in Example 1 above.

Example  3

In the preparation of the polyamic acid composition, a mixture of graphene / DMAc (1 mg ml -1) and a pure polyamic acid solution mixed with a suspension of graphene / DMAc (1 mg ml -1) so that the amount of reduced graphene oxide The polyimide film was completed in the same manner as in Example 1 above.

Example  4

In the preparation of the polyamic acid composition, a mixture of graphene / DMAc (1 mg ml -1) and a pure polyamic acid solution mixed with a suspension of graphene / DMAc (1 mg ml -1) so that the amount of reduced graphene oxide The polyimide film was completed in the same manner as in Example 1 above.

Example  5

A polyimide film was prepared in the same manner as in Example 1 except that hydrazine was used instead of N, N-dimethylformamide (DMF).

Example  6

A polyimide film was prepared in the same manner as in Example 1, except that L-ascorbic acid was used instead of N, N-dimethylformamide (DMF).

Comparative Example

Comparative Example  One

Unlike Example 1, a polyimide film was completed with a pure polyamic acid.

Comparative Example  2

A polyimide film was completed in the same manner as in Example 1 except that the polyimide film was completed with the unreduced graphene oxide after the oxidation in Example 1.

Experimental Example

< Experimental Example  One; Measurement of cross-sectional dispersion of polyimide film>

SEM images of polyimide films according to Examples 1, 5, 6 and Comparative Example 1 and Comparative Example 2 were observed to confirm whether the polyimide films were well dispersed. The shapes of Examples 1, 5, 6, and 1 and Comparative Example 2 were observed using FE-SEM (Hitachi S-4800). The results are shown in Fig.

As can be seen from FIG. 1, unlike Comparative Example 1, the cross-sections of Examples 1, 5, 6, and Comparative Example 2 showed good dispersion of the upper layer. Therefore, it can be confirmed that when the polyamic acid composition including the graphene oxide in which a part of the oxide groups is reduced through oxidation is made and the polyimide film is produced using the polyamic acid composition, the dispersion is well performed.

< Experimental Example  2; Measurement of facial dispersion of polyimide>

The polyimide films according to Example 1, Example 5, Example 6 and Comparative Example 2, which were well dispersed in cross section according to Experimental Example 1, were laminated by using a diamond knife and a Leica ultramicrotome to form a cross- And the inside of the polyimide film was confirmed by TEM. The results are shown in Fig.

As can be seen from FIG. 2, in all of the cases of Examples 1, 5, 6, and Comparative Example 2, it was confirmed that the dispersion of the inside was satisfactorily performed without any problem. Particularly, in the case of Example 5 and Example 6 in which hydrazine and L-ascorbic acid were used as a reducing agent, it was confirmed that the dispersion was better on the inner surface than in the other cases.

< Experimental Example  3; Mechanical strength measurement>

Experiments were conducted to measure the mechanical strengths of the respective polyimides according to Examples 1, 5, 6, and 1 and Comparative Example 2. The experiment was measured by UTM. The results are shown in Fig.

As can be seen from FIG. 3, it was confirmed that the physical properties of Examples 1, 5, 6 and Comparative Example 2 were improved compared with those of Comparative Example 1, which is a pure polyimide, and the mechanical strength was improved . Therefore, it was confirmed that when the polyimide was produced by dispersing the graphene oxide in the polyamic acid, the mechanical strength was improved.

< Experimental Example  4; Electrical conductivity measurement>

Experiments were conducted to measure the electrical conductivity of Examples 1, 5, 6, and Comparative Example 2, which were found to have excellent mechanical strength. This was measured using Hall Effect Measurement. The measurement results thereof are shown in Fig.

As shown in FIG. 4, it was confirmed that the electrical conductivities of Examples 1, 5, and 6, which were subjected to the reduction step, were superior to those of Comparative Example 2 where only the oxidation step was performed. As a result, it was confirmed that the polyimide films of Examples 1, 5 and 6, which had undergone the post-oxidation reduction process, were excellent in electrical conductivity and mechanical strength. It was also confirmed that the higher the content of reduced graphene oxide in the oxide group, the more gradually the electric conductivity was improved.

< Experimental Example  5; Graphene Oxide  Measurement of Mechanical Strength by Content>

Experiments were conducted to measure the mechanical strength change according to the contents of the graphene oxide in which some of the oxide groups were reduced in Examples 1, 2, 3 and 4. The experiment was carried out in the same manner as in Experimental Example 3, and the results are shown in FIG.

As can be seen from FIG. 5, in the case of Example 1 containing about 5 parts by weight of the reduced graphene oxide, it was confirmed that the most excellent mechanical strength was exhibited. In this case, it was confirmed that the mechanical strength was significantly increased from about 3 parts by weight in the case of Example 3, and the mechanical strength was lowered in the case of Example 4 or more, which was about 7 parts by weight as the case of Example 4. [ As can be seen from the SEM image of the polyimide cross section in FIG. 6, when the content of the graphene oxide exceeds 7 parts by weight, coagulation phenomenon occurs and it is confirmed that the mechanical strength is affected. Therefore, it was confirmed that the polyimide film having excellent electrical conductivity as the content of the graphene oxide is increased according to Experimental Example 4, but having a mechanical strength of 3 to 7 parts by weight can be provided.

< Experimental Example  6; XPS  Analysis results>

X-ray photoelectron spectroscopy (XPS) analysis was carried out in the case of Example 1, Example 5, Example 6, and Comparative Example 2. The XPS spectra were recorded using a VG Microtech 2000 ESCA system. The results are shown in Fig.

As can be seen from FIG. 7, a peak height was formed in the range of the binding energy (eV) of 550 to 580 eV in the case of Example 6 in comparison with the peak height according to the case of Comparative Example 2, which was about 70% or less It was confirmed that the peak height was formed at about 45% or less in the case of Example 1, and it was confirmed that the peak height was formed at about 20% or less in the case of Example 5. Therefore, it was confirmed that when the reducing agent according to the present invention is used, a peak height is formed at a maximum of 70% or less as compared with the case of Comparative Example 2. This means that the oxide group is reduced by 30% or more.

Taking the results of the above experiments into consideration, the polyimide film containing the graphene oxide only after the oxidation process has improved mechanical strength but hardly imparts electrical conductivity. However, it has been confirmed that the polyimide film comprising the polyamic acid composition including the graphene oxide in which some of the oxide groups have been reduced after the oxidation as in the above embodiment is a polyimide film having not only mechanical strength but also excellent electrical conductivity. Also, it was confirmed that when the content of the graphene oxide in which a part of the oxide groups is reduced is 3 to 7 parts by weight in the examples, a polyimide film having improved mechanical strength is produced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. It is natural.

Claims (11)

delete Wherein the oxide layer comprises a reduced amount of graphene oxide,
The graphene oxide in which a part of the oxide groups are reduced has a peak height of not more than 70% at a peak height formed at 550 to 580 eV when X-ray photoelectron spectroscopy (XPS) binding energy is measured against unreduced graphene oxide Lt; / RTI &
The reduction is performed with a reducing agent such as N, N-dimethylformamide (DMF)
And 5 parts by weight to 7 parts by weight of the partially reduced graphene oxide based on 100 parts by weight of the polyamic acid.
Wherein the oxide layer comprises a reduced amount of graphene oxide,
The graphene oxide in which a part of the oxide groups are reduced has a peak height of not more than 70% at a peak height formed at 550 to 580 eV when X-ray photoelectron spectroscopy (XPS) binding energy is measured against unreduced graphene oxide Lt; / RTI &
The reduction is carried out with a reducing agent such as L-ascorbic acid,
And 5 parts by weight to 7 parts by weight of the partially reduced graphene oxide based on 100 parts by weight of the polyamic acid.
A polyimide film comprising the polyamic acid composition according to claim 2 has a tensile modulus of 25 GPa or more, a tensile strength of 1100 Mpa or more, an elongation of 7.5% or more, and an electrical conductivity of 10 ^-5 Scm ^-1 or more. .
A polyimide film comprising the polyamic acid composition according to claim 3 has a tensile modulus of 10 Gpa or more, a tensile strength of 400 MPa or more, an elongation of 5% or more, and an electrical conductivity of 10 ^-1 Scm ^-1 or more. .
(1) oxidizing the graphite to produce graphene oxide;
(2) reducing a portion of the graphene oxide; And
(3) adding the partially reduced graphene oxide to the polyamic acid; Lt; / RTI &gt;
The reduction may be performed by reducing the oxide group of the graphene oxide by 30% to 80% with a reducing agent such as N, N-dimethylformamide (DMF)
And 5 parts by weight to 7 parts by weight of the partially reduced graphene oxide based on 100 parts by weight of the polyamic acid.
The method according to claim 6,
Further comprising the step of ultrasonically treating the graphene oxide to reduce the graphene oxide between the step (1) and the step (2).
The method according to claim 6,
And a heat treatment step at 50 to 250 ° C after the step (3).
delete (1) oxidizing the graphite to produce graphene oxide;
(2) reducing a portion of the graphene oxide; And
(3) adding the partially reduced graphene oxide to the polyamic acid; Lt; / RTI &gt;
The reduction may be performed by reducing the oxide group of the graphene oxide by 30% to 80% with L-ascorbic acid reducing agent,
And 5 parts by weight to 7 parts by weight of the partially reduced graphene oxide based on 100 parts by weight of the polyamic acid.

delete

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